1. Field of the Invention
This invention relates to a picture projection apparatus for projecting a picture displayed by spatial modulation means employing e.g., a liquid crystal panel.
2. Description of Related Art
Such picture projection apparatus is comprised of three liquid crystal panels 101a, 101b, 101c, as transmission type spatial modulation means, as shown in FIG. 1. In this picture projection apparatus, a light beam radiated from a light source 102, such as a halogen lamp, falls on a polarized light conversion system 104, through an integrator 103, to become a unidirectional linear-polarized light beam. The polarized light conversion system 104 includes a large number of polarized light beam splitters, a mirror and a xc2xd wavelength plate arranged in association with these polarized light beam splitters. In this polarized light conversion system 104, the light beam transmitted through the respective polarized light beam splitters are P-polarized light beams relative to the reflective surfaces of the polarized light beam splitters. The light beam reflected by the polarized light beam splitters are transmitted through the xc2xd wavelength plate to prove P-polarized light beam with respect to the reflective surfaces of the polarized light beam splitters.
A light beam through the polarized light conversion system 104 is reflected through a first condenser lens 105a by a first mirror 106a to fall on a first dichroic mirror 107a. In the light beam incident on this first dichroic mirror 107a, a first prime color component is transmitted, whilst the second and third prime color components are reflected. The first prime color component, transmitted through the first dichroic mirror 107a, is reflected by a second mirror 106a to fall through a second condenser lens 105b on a first liquid crystal panel 101a. This first liquid crystal panel 101a displays an image corresponding to the first prime color component to modulate the transmitted light in keeping with this image.
The second and third prime color components, reflected from the first dichroic mirror 107a, are incident on a second dichroic mirror 107b. In the light beam, incident on the second dichroic mirror 107b, the second prime color component is reflected, whilst the third prime color component is transmitted. The second prime color component, reflected by the second dichroic mirror 107b, falls through a third condenser lens 105c on the second liquid crystal panel 101b. This second liquid crystal panel 101b displays an image corresponding to the second prime color component and modulates the transmitted light in keeping with this image.
The third prime color component, transmitted through the second dichroic mirror 107b, is transmitted through a fourth condenser lens 105d, a third mirror 106c, a fifth condenser lens 105e, a fourth mirror 106d and a sixth condenser lens 105f in this order to fall on the third liquid crystal panel 101c. The third liquid crystal panel 101c displays an image corresponding to the third prime color component and modulates the transmitted light in keeping with the displayed image.
The light beams, transmitted through the first to third liquid crystal panels 101a to 101c, are incident from three directions on and synthesized by a dichroic prism 109 to exit from this dichroic prism 109. The light beam exiting from this dichroic prism 109 falls on a projection lens 110 so as to be projected on a screen, not shown. The light beam exiting from the dichroic prism 109 is synthesized from three prime color components, so that a color image is projected by a projection lens 110.
A certain known image projection device is made up of three liquid crystal panels 111a, 111b, 111c, as reflection type spatial modulation means, as shown in FIG. 2. In this image projection device, a light beam exiting from a light source 102 falls through an integrator 103 on the polarized light conversion system 104 to prove a unidirectional linear polarized light beam. The light beam transmitted through the polarized light conversion system 104 is reflected through the first condenser lens 105a by a mirror 106 so as to fall through the second condenser lens 105b on a polarizing beam splitter 112.
The incident light beam on the polarizing beam splitter 112 is an S-polarized light relative to the reflective surface of the polarizing beam splitter 112 and is reflected on a reflecting surface to fall on a first dichroic prism 113a. In the light beam, incident on the first dichroic prism 113a, the first prime color component is reflected on the inner prism surface, while the second and third prime color components are transmitted. The first prime color component, reflected by the inner surface of the first dichroic prism 113a, falls on the first liquid crystal panel 111a. This first liquid crystal panel 111a displays an image corresponding to the first prime color component and modulates and reflects the incident light in keeping with the image.
The second and third prime color components, transmitted through the first dichroic prism 113a, fall on the second dichroic prism 113b. In the light beam incident on the second dichroic prism 113b, the second prime color component is reflected by the inner prism surface, while the third prime color component is transmitted. The second prime color component, reflected by the inner surface of the second dichroic prism 113b, falls on the second liquid crystal panel 111b. This second liquid crystal panel 111b displays an image corresponding to the second prime color component and modulates and reflects the incident light in keeping with the image.
The third prime color component, transmitted through the second dichroic prism 113b, falls through the prism 113c on the third liquid crystal panel 111c. This third liquid crystal panel 111c displays an image corresponding to the third prime color component and modulates and reflects the incident light in keeping with the image.
The light beam, reflected by the first to third liquid crystal panels 111a to 111c, are synthesized by inversely following an optical path comprising the liquid crystal panels 111a, 111b and 111c to exit from the first dichroic prism 113a to fall on the polarizing bean splitter 112. The incident light beam on the polarizing beam splitter 112 is the p-polarized light relative to the reflecting surface of the polarizing beam splitter 112 and is transmitted through the reflecting surface to fall on the projection lens 110. The light beam exiting from the first dichroic prism 113a is synthesized from three prime color components, so that a color image is projected by a projection lens 110.
The image projection device is made up of three liquid crystal panels in order to display images corresponding to the three prime colors of red (R), green (G) and blue (B).
The above-described image projection device has many optical components, especially if it is provided with a transmission type liquid crystal panel, and hence is complex to assemble and fabricate. Moreover, if the liquid crystal panel is of the transmission type, the aperture ratio is low because of the necessity of providing the wiring etc.
If the reflection type liquid crystal panel is used, it is possible to reduce the size and to increase the aperture ratio as compared to the case in which the transmission type liquid crystal panel is used. However, if the reflection type liquid crystal panel is used, the length between the liquid crystal panel and the projection lens is increased as compared to the case in which the transmission type liquid crystal panel is used, with the back focus of the projection lens being longer. So, a projected image with a sufficient luminosity cannot be realized except if the diameters of the projection lens and the polarizing beam splitter are increased.
It is therefore an object of the present invention to provide an image projection apparatus which, with the reduced number of components, is easy to assemble and fabricate, which can be reduced in size and which allows to produce a projected image having sufficient luminosity.
In one aspect, the present invention provided an image projection apparatus including prime color component selection means made up of temporal color separation means and spatial color separation means, with the temporal color separation means removing one of prime color components and leaving the remaining two prime color components, in the incident light, the temporal color separation means sequentially changing the one prime color component as time elapses, the spatial color separation means separating the optical path of the one prime color component of the incident light from the optical path of the other two prime color components. The image projection apparatus also include modulation means made up of first spatial modulation means, on which falls one of split light beams, the optical path of which has been separated by the prime color component selection means, and second spatial modulation means, on which falls the other split light beam and projection means for synthesizing and projecting the light beams passed through the spatial modulation means in the modulation means. The first and second spatial modulation means performs spatial modulation on an image corresponding to one respectively different prime color component of the incident light in each operating state of the temporal color separation means.
An image projection apparatus according to the present invention includes a prime color component selection unit, made up of a temporal color separation sub-unit and a spatial color separation sub-unit, a modulation unit on which falls a light beam split in its optical path by the prime color component selection unit, and a projection unit for synthesizing and projecting the light beams from first and second spatial modulation sub-units of the modulation unit. In the image projection apparatus, the first and second spatial modulation sub-units perform spatial modulation on images corresponding to respective different prime color components. In the image projection apparatus of the present invention, two spatial modulation units are used, thus simplifying the structure and reducing the size as compared to the so-called three-plate type image projection apparatus employing three spatial modulation sub-units.
In this image projection apparatus, luminosity of the projected image equivalent to or superior to the xe2x80x9cthree plate typexe2x80x9d is realized, while color balance can be adjusted depending on coloration characteristics of the light source.
In this image projection apparatus, the problem of an edge color (color breakup), in the so-called field sequential color representation performing time division display of each prime color, can be alleviated.
That is, with the image projection apparatus of the present invention, the number of component parts can be reduced to provide for facilitated manufacture and small size as well as a to assure a projected image of sufficient lightness.